1. Field of the Invention
The present invention relates to a lens barrel which incorporates a guide mechanism using a cam groove(s) and a cam follower(s) which are respectively engaged in the cam groove(s).
2. Description of the Related Art
In a lens barrel which incorporates a guide mechanism using at least one cam groove and at least one cam follower which is engaged in the cam groove to move one or more elements of the lens barrel in a predetermined moving manner, there are various known methods of removing backlash and play between the cam follower and the cam groove to ensure a high positioning accuracy of one or more lens groups of the lens barrel. According to a simple method of removing such backlash and play, only a minimum clearance is established with a high degree of precision between each cam groove and the associated cam follower so that such backlash and play does not have to be taken into account. However, it is not practical to form the cam follower and the cam groove with such a high degree of precision in terms of the production cost, and also in time and effort.
If each cam groove extends in a direction inclined with respect to both the optical axis, of the lens system provided in the lens barrel, and a circumferential direction of the lens barrel, each cam groove can be considered to control forward and reverse rotations of either a follower member on which the cam follower is formed or a corresponding cam member on which the cam groove is appropriately formed in a manner so that each cam follower remains in contact with one of the opposite guide surfaces (guide surfaces) of the associated cam groove, between which the cam follower is positioned, for the purpose of guiding each cam follower along the associated cam groove with a high degree of precision. However, this method is not effective in removing backlash and play between the cam follower and specific portions of the cam groove which do not extend in a direction inclined with respect to both the optical axis of the lens system and a circumferential direction of the cam member, i.e., which extends only in a circumferential direction of the cam member, perpendicular to the optical axis.
In another method of removing backlash and play between the cam follower and the cam groove, a device for removing such backlash and play using one or more spring members as a biasing device is known in the art. However, it has formerly been difficult to simplify and miniaturize the structure of this conventional device. For instance, although the lens barrel needs to be provided around the aforementioned biasing device with a reaction force receiving portion (or portions) which receives the reaction force of the biasing device, the reaction force receiving portion tends to become a leading cause of an increase in size of the lens barrel because the reaction force receiving portion is designed as an independent member in conventional lens barrels. In addition, in such a conventional backlash and play removing device, a constant biasing force is applied between the cam groove and the cam follower regardless of whether the lens barrel is in use. Due to this structure, a large friction is produced between each cam groove and the associated cam follower even when backlash and play between the cam follower and the cam groove do not have to be reduced to a minimum, e.g., during the time the lens barrel changes its position from an accommodation position to a ready-to-photograph position in a zooming range (e.g., a wide-angle extremity) if the lens barrel is a zoom lens barrel. Such a large friction becomes an unfavorable resistance to the engagement between the cam follower and specific portions of the cam groove.
As another problem, if each cam follower bumps hard against one of the opposite guide surfaces of the associated cam groove due to an accidental impact (external force) on the lens barrel, a portion of each cam groove against which the associated cam follower bumps hard is damaged, thus making it impossible for the damaged cam groove to guide the associated cam follower smoothly afterwards.
The present invention provides a lens barrel which incorporates a guide mechanism using at least one cam groove and at least one cam follower which is engaged in the cam groove, wherein backlash and play between the cam groove and the cam follower can reliably be removed with a simple and small mechanism.
For example, a lens barrel including a ring member having a cam groove formed on an inner peripheral surface thereof, the cam groove including opposite guide surfaces; a lens support ring positioned in the ring member and supported thereby to be rotatable with respect to the ring member, the lens support ring having a first cam follower which is engaged in the cam groove of the ring member; a biasing ring coupled to the lens support ring to be movable in an optical axis direction and to be non-rotatable about the optical axis with respect to the lens support ring, the biasing ring having a second cam follower which is engaged in the cam groove of the ring member; and a biasing device for biasing the lens support ring and the biasing ring in opposite directions in the optical axis direction to press the first cam follower and the second cam follower against the opposite guide surfaces of the cam groove.
It is desirable for the biasing device to bias the lens support ring and the biasing ring in opposite directions away from each other in the optical axis direction.
It is desirable for the opposite guide surfaces of the cam groove to include a front guide surface and a rear guide surface, the front guide surface being provided at a forward position of the optical axis and the rear guide surface being provided at a rearward position of the optical axis. The first cam follower is pressed against the front guide surface and the second cam follower is pressed against the rear guide surface.
It is desirable for the first cam follower to be formed on an outer peripheral surface of the lens support ring, at a rear end thereof in the optical axis direction. A radial end portion of the first cam follower is engaged in the cam groove, and a base portion of the first cam follower is fitted in a recess formed on the biasing ring.
It is desirable for the first cam follower and the second cam follower to be pressed against one of the opposite guide surfaces and the other of the opposite guide surfaces, respectively, with the first cam follower and the second cam follower not being in contact with the other of the opposite guide surfaces and the one of the opposite guide surfaces, respectively.
It is desirable for a mutual distance in the optical axis direction between the first cam follower and the second cam follower to change in accordance with movement of the first and second cam followers along the cam groove.
The lens barrel can include a zoom lens barrel. It is desirable for the cam groove to include a zooming groove portion used to change a position of the zoom lens barrel between a telephoto extremity and a wide-angle extremity, and a photographing preparation groove portion which extends from one end of the zooming groove portion to an accommodation position. The mutual distance between the first and second cam followers when the first and second cam followers are engaged in the photographing-preparation groove portion is greater than when the first and second cam followers are engaged in the zooming groove portion.
It is desirable for the zooming groove portion to extend only in a circumferential direction of the lens support ring, perpendicular to the optical axis. It is desirable for the photographing-preparation groove portion extends in a direction inclined with respect to both the optical axis and the circumferential direction of the lens support ring. The first cam follower and the second cam follower are engaged in the cam groove at different circumferential positions of the lens support ring.
The ring member includes a stationary barrel fixed to a camera body, the lens barrel further including a rotation transfer ring via which a rotational motion is transferred to the lens support ring, the rotation transfer ring being supported by the ring member so as to be immovable in the optical axis direction and to be rotatable about the optical axis with respect to the ring member.
It is desirable for the rotation transfer ring to be engaged with the lens support ring and the biasing ring to be non-rotatable with respect to both the lens support ring and the biasing ring.
The biasing device can include at least one compression spring provided between the lens support ring and the biasing ring.
The lens barrel can further include a motor which generates the rotational motion, so that the rotation transfer ring transfers the rotational motion from the motor to the lens support ring.
The lens support ring can include a plurality of first cam grooves and a plurality of second cam grooves which are formed on an inner peripheral surface of the lens support ring and an outer peripheral surface of the lens support ring, respectively.
The present disclosure relates to subject matter contained in Japanese Patent Application No.2001-335565 (filed on Oct. 31, 2001) which is expressly incorporated herein by reference in its entirety.